Polycarbonate polymers are known as being excellent molding materials since products made therefrom exhibit such properties as high impact strength, toughness, high transparency, wide temperature limits (high impact resistance below -60.degree. C. and a UL thermal endurance rating of 115.degree. C. with impact), good dimensional stability, good creep resistance, and the like. It would be desirable to add to this list of properties that of resistance to high heat distortion thereby enabling these aromatic polycarbonates to also be used to form molded components that will be exposed to elevated temperature environments such as components exposed to automobile and airplane engines, and the like.
It is known to obtain polycarbonates which contain halogenated monomers as their main, polymeric building blocks. For example, U.S. Pat. No. 3,028,365 discloses a host of polycarbonate compositions including tetrabromobisphenol-A and a dichloromethylenediphenol monomer, as well as processes for obtaining these polycarbonates.
U.S. Pat. No. 3,062,781 discloses that halogenated polycarbonates can be obtained by first halogenating a diphenol containing at least two halogen substituents. However, the only dihalogenated diphenol disclosed is dichlorobisphenol-A.
German Pat. No. P25 20 317.2 discloses that halogenated polycarbonates can be obtained by halogenating bisphenol-A (4,4'-isopropylidenediphenol) to produce a mixture of unreacted bisphenol-A and statistical mixtures of halogenated bisphenol-A (BPA). The halogenated bisphenols disclosed comprise, primarily, tri- and tetrahalogenated BPA.
In general, these prior art references recognize that flame retardance can be imparted to polycarbonates by halogenating the monomeric building blocks from which they are obtained. None of these references, however, discloses or suggests that a high molecular weight polycarbonate resin having resistance to high heat distortion as well as improved flame retardance can be obtained from a particular dihalogenated diphenol.